使用Java中的两个线程按递增顺序打印偶数和奇数

先决条件： 多线程

给定一个整数N，任务是编写Java程序以使用两个线程按升序打印前N个自然数。

例子：

Input: N = 10
Output: 1 2 3 4 5 6 7 8 9 10

Input: N = 18
Output: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

方法：这个想法是创建两个线程，用一个线程打印偶数，用另一个线程打印奇数。以下是步骤：

• 使用以下语法创建两个线程T1和T2 ，其中T1和T2分别用于打印奇数和偶数。
  

  Thread T1 = new Thread(new Runnable() {
             public void run() { mt.printEvenNumber(); }
  });

  Thread T2 = new Thread(new Runnable() {
             public void run() { mt.printOddNumber(); }
  });

  where,
  printOddNumber() is used to print all the odd numbers till N,
  printEvenNumber() is used to print all the even numbers till N.

• 维护一个全局计数器变量并使用以下函数启动两个线程：
  

  T1.start();
  T2.start();

• 如果计数器在线程T1中是偶数，则等待线程T2打印该偶数。否则，打印该奇数，递增计数器并使用函数notify() 通知线程T2 。
• 如果线程T2中的计数器为奇数，则等待线程T1打印该奇数。否则，打印该偶数，递增计数器并使用函数notify() 通知线程T1 。

下面是上述方法的实现：

Java

// Java program for the above approach
  
public class GFG {
  
    // Starting counter
    int counter = 1;
  
    static int N;
  
    // Function to print odd numbers
    public void printOddNumber()
    {
        synchronized (this)
        {
            // Print number till the N
            while (counter < N) {
  
                // If count is even then print
                while (counter % 2 == 0) {
  
                    // Exception handle
                    try {
                        wait();
                    }
                    catch (
                        InterruptedException e) {
                        e.printStackTrace();
                    }
                }
  
                // Print the number
                System.out.print(counter + " ");
  
                // Increment counter
                counter++;
  
                // Notify to second thread
                notify();
            }
        }
    }
  
    // Function to print even numbers
    public void printEvenNumber()
    {
        synchronized (this)
        {
            // Print number till the N
            while (counter < N) {
  
                // If count is odd then print
                while (counter % 2 == 1) {
  
                    // Exception handle
                    try {
                        wait();
                    }
                    catch (
                        InterruptedException e) {
                        e.printStackTrace();
                    }
                }
  
                // Print the number
                System.out.print(
                    counter + " ");
  
                // Increment counter
                counter++;
  
                // Notify to 2nd thread
                notify();
            }
        }
    }
  
    // Driver Code
    public static void main(String[] args)
    {
        // Given Number N
        N = 10;
  
        // Create an object of class
        GFG mt = new GFG();
  
        // Create thread t1
        Thread t1 = new Thread(new Runnable() {
            public void run()
            {
                mt.printEvenNumber();
            }
        });
  
        // Create thread t2
        Thread t2 = new Thread(new Runnable() {
            public void run()
            {
                mt.printOddNumber();
            }
        });
  
        // Start both threads
        t1.start();
        t2.start();
    }
}

输出：

1 2 3 4 5 6 7 8 9 10

时间复杂度： O(N)
辅助空间： O(1)